My car keeps overheating. We've changed the thermostat, coolant and radiator. None worked. What's next?

Question

It overheats when I climb hills, but ib town it's fine.

Answer 1

Well there are any number of things that can make a car overheat, but if you will tolerate it, I will try to explain how the cooling system works and along the way point you toward some potential things to look at in your search for the problem.

The system basically circulates coolant to the engine via hoses from the radiator and with the assistance of a water pump to drive the coolant through it. That pump is driven by a belt.

Now, as the engine operates best at a relatively constant temperature, a thermostat is added that essentially is a temperature controlled valve, manufactured to open at a particular setting, say 190 degrees farenheit.

The engine has journals (or cast passages as it were) in the sides of the block and cylinder head to allow for a cooling bath to be evenly distributed to carry away heat. When the temperature reaches 190 degrees (or whatever temperature the thermostat is designed to trigger) the thermostat opens and allows the water pump to pump cooler coolant from the radiator into the journals of the block and head, displacing the warmer coolant which goes back to the radiator to be cooled down. Then the thermostat closes and the process repeats itself.

Incidentally, as the water pump runs all of the time, when the thermostat is closed it shunts this circulation into a bypass and back to radiator immediately.

Now the radiator simply has a number of tubes in it that are surrounded by thin aluminum or copper fins that help dissipate heat, and as air passes throught it these fins serve to carry heat off of the tubes containing the hot coolant for the air to carry away.

So, you have replaced the radiator, and the coolant and the thermostat, and logically one might look to the one remaining component, the water pump, which, if it is marginal could be the problem. However, usually when a water pump fails it also leaks and it would be unusual (but not impossible) for it to be operating just well enough to keep the car from overheating when the engine is not under the added heat strain of climbing a hill, but otherwise showing no overt signs of failure by leaking. Accordingly, I would look to a couple of other things.

One is mixture of coolant and water that you used when you replaced the coolant. Antifreeze itself is an excellent rust inhibitor and very good at preventing the water from freezing up in the winter, but in reality is not much of a coolant. Water is far better at carrying away heat, but is corrosive in and of itself and freezes at relatively high temperatures--hence the need for anti-freeze. However, all things in proportion, and if you used too much antifreeze and not enough water you may have limited your system's capacity to cool. Any gas station can check that for you and usually free of charge.

In addition, when you changed the coolant, you may not have refilled the system properly, allowing an air gap to accumulate in the cylinder head at the high point in the system which is not allowing coolant to reach there. Most engines have a bleeder bolt or bolts located somewhere on the cylinder head that can be removed to let out any air trapped at the high points in the system and you can remove these and top off the journals to eliminate the air gaps.

Still another possibility is a blown head gasket. The head gasket is a gasket between the block and the cylinder head that helps to seal the two together when the head is bolted on, and it has holes in it that coincide with the coolant passages and oil passages (not to mention the cylinders themselves) so that the fluids cannot mix and to seal in compression in the cylinders themselves. If this gasket is breached you will usually see evidence of it in oil drops floating in your coolant or coolant drops or sludge on the oil dipstick. As you did not comment on that this problem seems less likely.

Finally, as one of your commentators mentioned, it could be your cooling fan or fans, or the thermostatic switch that causes them to turn on, but I would doubt this, as you indicated the car was overheating climbing hills, which would necessarily mean you are moving. Normally air flow is sufficient when you are moving that the fans are not needed unless you are moving very slowly. And if the fans were not working, you would not need a hill to make the car overheat, it would do so simply by sitting still for a few minutes.

Anyway, I hope this has been helpful. If you wish to consult further, please do not hesitate to contact me at [e-mail].

Answer 2

The bad in traffic, okay on the freeway, points strongly to an airflow problem with a lesser possibility of a water flow problem. You don't mention make, model or year, so here are the two scenarios: If the fan is belt driven it probably has a fan clutch, a finned aluminum tuna can shaped thing that the fan mounts to. Those are high failure rate items, and if you have one you can check it by trying to turn the fan by hand when the engine is off. It should not spin more than about an inch if you try to spin the fan but it should move smoothly. If the fan is electric, I bet it doesn't run. Common failures there are the fan motor, the relay that controls the fan, or the sensor that controls the relay that controls the fan that cools the radiator in the car that Jack drives. Sorry - got carried away.

Answer 3

I will said your car has a crack on the head or maybe is warp because an overheating before. Aluminum engines can crack in OH , they my have to take the head out and check for a flow. See if you have some water on your oil , check the oil level. if all this is the case you will need a new head on your engine some times can be welded no warrantied that will last depends where is the crack. @ i hope this will help you to know what to do.

Answer 4

I'd check to see if the fan, or fans are coming on when the engine gets hot. ANother way to test them, is to unplug the coolant temp sensor. When you do that, the fans will come on automatically. If not, then that means the fan, or both fans are gone. Changing a wate pump, on your car, will require taking off that timing belt. Worst case there.

Answer 5

It could be the propellers in the water pump, but that is kind of unlikely, it can be your clutch fan if it is manual driven or your electric fans if electric, it can also be caused by a very dirty engine, grease and/or mud over your block and oil pan, it won't let the engine disipate heat properly. It could also be out of time, but if it is running really good that probably isn't it. Good luck.

Answer 6

water pumps arent too expensive, i got one refurbished at autozone for $60. also check the fan liek someone said already. my dads intrepid was actually doing that in traffic and all he did was replace the thermostat, make sure yours is in good working condition. also, if it ever happens to you when driving, turn your heat all the way up and open your windows. yes it get really really REALLY hot in the car but u gotta do what you gotta do. or pull over wherever you can.

Answer 7

turn off the Air Conditioner on the hill, also, u might wanna try going slower and not tow anything.

Answer 8

Have your water pump checked it sound like it's going bad.Good Luck!

Answer 9

Bad waterpump and/or cooling fan also check your sensors in the fusebox make sure that they arent burnt

Answer 10

Water pump?